In semiconductor packaging technologies, flip-chip is the most promising type of packaging method. Related arts and patents have been constantly brought up to propose various improved methods. Among these flip-chip packaging methods, the methods using printing and metal jetting bumping process are the most competitive ones due to their lower costs. However, when these methods are applied to the fine pitch bumping process, short circuit or high junction resistance due to solder joint bridging or missing phenomenon frequently happens. It causes the reliability issues of the packaged IC devices, and reduces the yield of the packaging process.
Anisotropic conductive film (ACF) is composed of conductive particles and polymer resin. It provides both electrical and mechanical interconnections between a chip and a substrate, and offers numerous advantages over traditional solders, including flexible and simple process at low temperature, fluxless formulations and friendliness to environment (lead free process). But due to the size limitation of the conductive particles, when the distances between the bumps on the chip or substrate are too small, the anisotropic conductive property no longer exists due to the conduction along the X-Y direction and all of the signals within the IC device are bridged. For the fine pitch interconnection with electrically conductive adhesive, arranging the conductive particles regularly within the polymer matrix is one of the methods to solving the problem which is mentioned above. The regular arrangement of the conductive particles is achieved mostly by using masks to uniformly distribute the conductive particles or disperse the conductive particles only on certain areas of the chip or substrate. An adhesive insulation layer is then coated to fix the conductive particles.
U.S. Pat. No. 5,221,417 teaches a method using external magnetic field to selectively disperse conductive particles to form an anisotropic conductive film. In this method, a layer of ferromagnetic film is first coated on a temporary substrate. The ferromagnetic film is then patterned using a photo-lithographic etching process. An external magnetic field is then applied so that the ferromagnetic film is magnetized with a polarity. Subsequently, conductive particles are dispersed on the ferromagnetic film. As the ferromagnetic film is magnetized, the conductive particles are only collected on the pattern of the ferromagnetic film. The conductive particles are then brought into contact with and thereby adhered to an adhesive layer on a substrate. An anisotropic conductive film with uniformly distributed conductive particles is obtained subsequently after removing the temporary substrate and ferromagnetic film. The foregoing method taught by the U.S. Pat. No. 5,221,417 is more costly as additional ferromagnetic film and photo-lithographic etching process are required. In addition, conductive particles would be stacked along the Z direction.
U.S. Pat. No. 6,042,894 teaches a method using a screen with pores to uniformly disperse conductive particles. In this method, conductive particles are given charges induced either by a strong electric field within a dry environment or by contacting with a roller or brash having a strong electric field. The screen is then applied with an opposite electric field to attract the conductive particles with charges to pass through the pores and fall on a sticking layer of a substrate. An anisotropic conductive film with uniformly distributed conductive particles is thereby obtained. As conductive particles are with charges of same electricity, a stacking of conductive particles along the Z direction is thereby avoided. However, the foregoing method is complicated, difficult to operate, and costly. Moreover, as the diameter of the conductive particles is reduced, the pores of the screen have to be shrunk and the cost for producing the screen is increased as well.
The two aforementioned methods for uniformly arranging conductive particles both first fix the conductive particles in a bonding film, then bond another chip to establish electrical connections. The present invention provides a method to uniformly and regularly fix the conductive particles on the bumps of a chip. Then a non-conductive bonding film is used to join the chip with another chip. The method provided by the present invention can not only reduce the production cost significantly, but also greatly increase the yield of bonding chips.